Influence of abutment macro- and micro-geometry on morphologic and morphometric features of peri-implant connective tissue

Objectives: The aim of the present human observational study is to provide morphologic and morphometric analysis of peri-implant connective tissue next to abutments with divergent or convergent macro-geometry and different surface micro-characteristics. Materials and Methods: Thirty patients were rehabilitated with single implants in the posterior area and one out of three different healing abutments with a one stage technique: machined divergent abutment (DIV-MAC), machined convergent abutment (CONV-MAC) or convergent abutment with ultrathin threaded surface (CONV-UTM). At 3 months post implant insertion peri-implant soft tissue was harvested; the following outcomes were investigated: histomorphometry (vertical width of connective and epithelial components) as detected by histology and polarized light; connective tissue vertical width and 3D organization as detected by synchrotron-based high-resolution phase-contrast based tomography (PhC-µCT). Results: Significant differences in connective tissue vertical dimension (aJE-AM) were found between DIV-MAC and both CONV-MAC and CONV-UTM, both by histology and PhC-µCT, with significantly higher values for the last two groups. Moreover, 2D histological analysis did not find significant differences in the junctional epithelium vertical dimension (PM-aJE). Importantly, PhC-µCT analysis revealed, at 3D level, significant greater amount and density of collagen bundles for CONV-UTM compared with the other two groups. Conclusions: Convergent abutment profiles, regardless of their surface micro-geometry, seem to favour axial development of peri-implant connective tissue. Moreover, ultrathin threaded surfaces seem associated with denser and greater connective tissue organization, which might improve peri-implant soft tissue seal.